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II. To repeat the experiments of Klaproth relating to the conversion of water into steam, by highly heated metal, and to make others calculated to show whether, under any circumstances, intensely heated metal can produce, suddenly, great quantities of highly elastic steam:
The first part of this query relates to the repetition and extension of the experiments of Klaproth, the second has reference to them, but may be determined by direct experiment, independently of the methods required for obtaining an answer to the first part of the query. It has been supposed that because the metal of a boiler was heated above the temperature at which the metal would produce steam most rapidly, it was impossible to account for the production of quantities of highly elastic steam, by such a cause. The committee, determined to make the fact of the production of high steam by intensely heated metal the subject of a direct experiment, and under circumstances as nearly similar as possible to those which may occur in a boiler, of which some parts, as the sides or interior flues, may become unduly heated, when not in contact with water.
The experimental boiler being arranged as already described, a small quantity of water was placed in it and boiled away; the heat being still applied, the temperature of the bottom was gradually raised. At different temperatures of the bottom, water was thrown in by the forcing pump, and the effect of a given quantity, on the gauge, noted. The temperature of the steam generated, was ascertained by a thermometer passing horizontally through the back head g, Plate 1, and two-thirds of the diameter above the bottom of the boiler: a second horizontal thermometer as near to the bottom as the rim of the boiler would permit, served to show whether the heat was rising or falling, and was noted for this purpose. Both the windows of the boiler had glass ths of an inch thick in them, without the cross bar covering. The water injected was at 70° Fah. The course of the water injected could be distinctly marked after the bottom of the boiler had become heated to redness, and was examined through the glass window d, Plate 3. The force of the pump carried it to the fire end, nearly; the boiler being slightly inclined to the back end, the water slid back in one or more dark masses, moving down the central line, or diverted up the sides, greatly agitated and frequently changing its shape. The water generally disappeared at the back end, though parts were retained by accidental spots of sediment, and disappeared upon them. The table below gives the results of the second day's experiments on this subject; they were terminated by violently bursting out the glass window at the fire end of the boiler.
The height of the lower thermometer, as noted by an observer at the back end of the boiler, is given in the first column of the table, with the appearance of the bottom of the boiler, both being examined before injecting water. The gauge was allowed to fall to the height denoting one atmosphere, before giving the number of strokes of the pump, from which the quantities of water, in the third column, are taken. The pressures in the fourth column were noted on the gauge by the same experimenter, who threw in the water. The first effect was examined through the back window, D, Plate 3, and the temperature of the steam produced, before the gauge began to fall, was noted as is recorded in the fifth column. As in all the experiments, the steam was rapidly produced, and the total effect was the object sought, the time was no further noticed than to ascertain that accidental circumstances independent of the temperature, rendered the total time of evaporation very variable, and that the maximum of effect was always passed in the space of from one to four or five minutes.
In the last experiment, the glass window at the fire end of the boiler, blew out with a quick sharp report, as loud as that of a musket; the fragments of glass, from a hole in the centre of the plate, were projected through a window, about three feet from the boiler, and could not be found. The number for twelve atmospheres is placed opposite to this experiment, as being an approximate result. In the act of observing the gauge, the glass burst, and the mercury at once fell: the number of inches at which the mercury had certainly risen, and above which it was, by an undetermined quantity, not, however, very considerable, was noted; and from this the pressure given in the table, is calculated. Here explosive steam was generated by the injection of water upon red hot iron, and in a time not exceeding one or two minutes at the most, the interval between the last stroke of the pump and the explosion, not having been sufficient to note the height of the gauge; the experimenter being at the pump, which was adjacent to the gauge.
By comparing the temperature of the steam in these experiments, with its observed pressure, it will be seen, that in not one of them was water enough injected to give the steam a density even approaching to that corresponding to its temperature: for example, 336°, F., should give a pressure of nearly 7 atmospheres, instead of 3.3, the observed pressure; 388° should give more than 14* atmospheres, instead of 8.2 and 448°; about 27 atmospheres, instead of 10. The violence of the effect was not, therefore, carried as far as it might have been, the metal not having been cooled down as far as it might have been, to produce the greatest effect; and yet, within two minutes the pressure was changed from one to twelve atmospheres.
The rise of temperature shown in the first column, serves to prove, that by successive introductions of water, the metal was not so far deprived of heat as to be cooled towards the point of maximum vaporization, but that the results were obtained with metal heated to redness."
A similar experiment to these was made by our countryman, Perkins, but surcharged steam being present in the vessel into which heated water was
Arago and Dulong.
forced, it was to the action of this that he attributed his result. This opinion will be examined subsequently, but the attributed source of action was present only in a very attenuated state, if at all, at the beginning of each experiment made by the committee.
The repetition, and extension, of the experiments of Klaproth, was one of the most laborious of the undertakings of the committee, and the results will be found in a future article of the report.
III. To ascertain whether intensely heated and unsaturated steam can, by the projection of water into it, produce highly elastic vapour.
The supposition that water, thrown into hot and unsaturated steam, is flashed into highly elastic vapour, forms the basis of the theory of the explosion of steam-boilers, of our countryman, Perkins; a theory which has been em. braced by many; and which, though shown to be contrary to the deductions from the well established laws of heat, is not now without its advocates. It seemed to the committee interesting to appeal to direct experiment upon this point, and thus to ascertain whether any circumstances, not embraced in the general view of the theory, existed; or whether all the circumstances had been rightly estimated, and the conclusions drawn from the application of the general laws of heat would be confirmed. Being unwilling to incur any conside rable expenditure in this branch of their inquiry, the experiments were rendered uncomfortable beyond any thing which occurred in their other researches. The means of producing the unsaturated steam were these: a row of bricks was removed from the top of the furnace, and near to the boiler, thus laying bare nearly half the convex surface of the latter (five inches from the top). By building on the sides of the top of the furnace, with bricks, loosely arranged, a space was formed for placing fuel, having the boiler for its bottom, and bounded by the bricks on its sides. A cap of sheet iron above, served to promote the draught and to carry off much of the deleterious gas produced by the charcoal used as fuel. The fusible plate apparatus was removed from the boiler, to prevent injury, and the safety valve was surrounded by a tin to keep the fuel from contact with the valve. By filling the boiler about half full of water, and applying heat below, to raise the water to any required temperature, the upper half of the boiler would be filled with steam of an elasticity due to that temperature, this elasticity being measured by the gauge. Fire being now placed upon the top would heat the metal of the upper half of the boiler; and this, by communicating its heat to the steam, would surcharge the latter. To measure the temperature, thus acquired by the steam, as well as that of the water below it, thermometers were placed in the iron tubes already described; the mercury was removed from the tubes, except enough to cover the bulbs of the thermometers, so that the temperature shown by them might be, as nearly as possible, that of the steam by which the shorter tube was surrounded, and of the water, into which the longer tube dipped. The scales of these instruments were protected from the fire, by surrounding them, at some distance, by tin plates. The scales were of seasoned box wood, the refinement of a correction for the errors of the instruments was not considered to be at all required by the nature of the research, the results of which errors, even a few degrees of temperature would not materially affect. In the final experiments, on this subject, the thermometers, with metallic scales, and surrounded by water, were put in place. The apparatus for injecting water, consisted of a tube attached to the stop-cock, v, Plate 1, on the back head of the boiler, and which communicated with the forcing pump; the tube terminated in a spherical segment, in which fourteen holes, each of the size of a cambric needle, were made; through these the water was forced in spray. By exami nation it appeared that the small stream, from the highest hole, struck the top of the boiler near the safety valve; that two or three struck the front head; VOL. XVII.-No. 1.-JANUARY, 1836.
two or three the water in the boiler, near the back head, leaving from seven to nine apertures, the water from which crossed the steam chamber in an inclined and very effective direction. The effect of the streams from the three or four apertures, first spoken of, would be, if they were not taken up by the steam, to vitiate, in degree, the experiments, by striking the top and end of the boiler. With the openings, thus described, the first day's experiments on this subject were made. The heat of the surcharged steam could not, with the arrangements then provided, be raised above 484 degrees. The method of experimenting, having been the same as was subsequently used, may as well be stated in this place. The fire having been applied below the boiler, the water was heated to a temperature corresponding to from one and a half to two and a half atmospheres; the coals were then, in part, removed to the top of the boiler, fresh fuel being supplied below: the effect of the heat applied above was soon visible upon the thermometer in the steam, and upon the gauge. When the temperature of the surcharged steam sufficiently surpassed that of the water, as shown by the larger thermometer, the injection of water was commenced, the injection pipe being carefully kept cool by wet sponges and cloths. The temperature of the thermometers in the water and steam, were noticed both before and after the injection, by one experimenter, while a second made the requisite number of strokes of the forcing pump, observed the indications of the steam gauge, and when the experiment was concluded, gave the quantity of water used. The temperature of the air in the gauge was noted from time to time. The apertures in both the heads were secured with metallic plates, to prevent leakage through them.
On the second day, six of the fourteen small holes were plugged up, that the source of error, already mentioned, might not exist. The temperature attained by the surcharged steam was 440°, at, and below which, experiments mere made. The general nature of the results, obtained on the first and second days, coincide, allowing for the difference of circumstances, so entirely with those of the final trial, when a satisfactory temperature was obtained in the surcharged steam, that it would be uninteresting to detail them. The same remark may be made of subsequent trials.
As the quantity of water thrown in, during all these experiments, was small, it was considered advisable to increase it, in order that more marked effects might be obtained; this was done by removing the pierced head from the pipe, thus delivering nearly the full capacity of the pump at each stroke. The quantity of water thus injected through the steam by each stroke of the pump, was, at a mean, half a fluid ounce. No heating of the injection water was required, as the heat necessary to raise water from the temperature of the experiments to the boiling point was but a small fraction of that required to convert it into steam.
In the last day of trial the heat of the top of the boiler was so great and so long sustained, that the thermometer in the water became, in the course of the experiments, for reasons which will be stated, comparatively useless, as an indicator of the temperature of the water. The following tabular view of the results of the experiments is extracted from the minutes. The first column of the table contains the temperature of the surcharged steam, previous to the injection of water in any experiment, the second column that after the injection, this comparison being made to ascertain whether the heat supplied was, or was not, sufficient to make up for that consumed in vaporizing the water thrown in. The third column shows the quantity of water injected; the fourth the height of the gauge before the experiment; the fifth the height after the experiment; the sixth the temperature of the gauge; the seventh and eighth, the pressures in atmospheres, calculated from the height of the gauge, and the temperature of the air within it, before and after each experi